This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-080851 filed on Mar. 22, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to vehicle braking systems. More particularly, the present invention pertains to a braking control apparatus for vehicles which is adapted to generate a master cylinder pressure in response to a pedal depression force and to automatically increase the master cylinder pressure through operation of a booster.
One known braking control apparatus is disclosed in German Patent Offenlegungsschrift No. 197 03 776 A1. This braking control apparatus includes a fluid pressure generating device for generating a master cylinder pressure in response to a pedal depression force and a pressurizing device for introducing fluid pressure to a pressure chamber of the fluid pressure generating device in order to obtain a boosted force for the pedal depression force by automatically increasing the master cylinder pressure by the pressurizing device.
With this known braking control apparatus, it is necessary to check the automatic pressure increasing function to assess whether it is correctly calculated before starting the vehicle so that the increased pressure is always assured without giving any undesired feeling to the driver of the vehicle.
A need thus exists for a vehicle braking control apparatus that is able to readily and reliably check the automatic pressure increase function and assess whether it is calculated correctly when the vehicle starts.
A braking control apparatus for a vehicle includes a fluid pressure generator that generates a master cylinder pressure in a master cylinder in response to a pedal depression force, a fluid supplying device that supplies braking fluid pressure to wheel cylinders of each wheel of the vehicle from the master cylinder, a pressure apply device that introduces fluid pressure to the pressure chamber of the fluid pressure generator, and a controller that automatically increases the master cylinder pressure by controlling the pressure apply device and for controlling the braking force of each wheel by driving the fluid supplying device. The controller includes a pressure apply check device for starting pressure apply check when the vehicle is started to determine whether the automatic pressure increase function is properly performed. The pressure apply check device judges that the proper automatic pressure increase is made when the master cylinder pressure is increased to a predetermined value within a predetermined time after the pressure apply check starts.
According to the present invention, the pressure apply check is performed when the vehicle is started because the pressure apply check is started in synchronization with the starting of the vehicle. Additionally, in the pressure apply check device, the automatic pressure apply is judged normal when the master cylinder pressure is increased up to the fixed value. The pressure apply check device is able to detect an abnormality of the automatic pressure apply caused by a failure in the pressure apply device when the master cylinder pressure is not increased up to the fixed value.
The braking control apparatus also includes a brake pedal depression force device that outputs a first signal when the brake pedal is depressed and outputs a second signal when the brake pedal is released. The pressure apply check device starts the pressure apply check when the second signal is outputted after an initial first signal has been outputted after the engine is started. The pressure apply check device holds the brake fluid pressure of the wheel cylinders of each wheel by maintaining the fluid supply device in a holding condition and starts automatic pressure increase operation by controlling the pressure apply device at the start of the pressure apply check.
Thus, the increasing of the master cylinder pressure by the automatic pressure apply is not transmitted to the wheel cylinders and the pressure apply check can be practiced without disturbing the vehicle start because the brake fluid of the wheel cylinders of all the wheels is assured when the pressure apply check is started.
The pressure apply check device ends the pressure apply check when the first signal is outputted during the pressure apply check. Thus, when the applied check is practiced after the vehicle actually starts, if the brake pedal is depressed by the deceleration demand of the driver, the pressure apply check is ended and the deceleration demand is performed.
The pressure apply check means ends the pressure apply check when the changing speed of the master cylinder pressure becomes zero during the pressure apply check, A learning process correction of a pre-set pressure modulating characteristic of the pressure apply device is then performed based on the control current value to the linear valve and the master cylinder pressure. Because the correction of the pressure control or modulating characteristic is performed based on the stable master cylinder pressure when the master cylinder pressure is increased and the pressure changing speed becomes zero and based on the control current value to the linear valve, the subsequent automatic pressure apply control carried out more correctly.
According to another aspect of the invention, a braking control apparatus for a vehicle includes a master cylinder generating a brake fluid pressure in response to a brake pedal depression force, with the master cylinder including a pressure chamber connected to at least one wheel cylinder associated with one of the wheels, a fluid pressure sensor detecting the master cylinder pressure in the pressure chamber, a pressure apply unit performing pressure apply by introducing fluid pressure to the pressure chamber of the master cylinder, a controller automatically increasing the brake fluid pressure by controlling the pressure apply unit, and a pressure apply check device for starting a pressure apply check when the vehicle is started to determine whether the pressure apply is abnormal. The he pressure apply check device determines that the pressure apply is abnormal when the master cylinder pressure determined by the fluid pressure sensor fails to reach a predetermined value within a predetermined time.
Another aspect of the invention involves a method for determining proper automatic pressure increase in a braking control apparatus for a vehicle that includes an engine, a brake pedal, wheels, a master cylinder that generates a master cylinder pressure in response to depression of the brake pedal, and a pressure apply unit for introducing fluid pressure into a pressure chamber of the master cylinder to effect automatic pressure increase. The method includes initiating a pressure apply check upon starting the vehicle to determine that the automatic pressure increase is proper, measuring the master cylinder pressure after initiation of the pressure apply check, and determining that the automatic pressure increase is proper when the master cylinder pressure has reached a predetermined value within a predetermined time after initiation of the pressure apply check.